Patent GB-889604-A (GB)
Title: Improvements in or relating to signalling systems for the control of street traffic
Inventor: RANGE ALAN LESLIE
IPC: G08G1/081
Filed: 1959-06-26
Abstract: 889,604. Road signals for controlling traffic. AUTOMATIC TELEPHONE & ELECTRIC CO. Ltd. May 4, 1960 [June 26, 1959], No. 21932/59. Class 118. In a system in which a number of local controllers are controlled by a master controller to provide linked working throughout a district, control pulses are sent simultaneously during each cycle to all the local controllers in accordance with one of several possible time plans, and offset timers in each local controller determine how soon after the receipt of the control pulses the appropriate control is to take effect. Local controller, Figs. 1-4, operating independently.-A pair of switches SA, SB which step under the control of timing circuits are provided for controlling the main phases A and B. When the power which consists of unsmoothed rectified A.C. is switched on, relay N energizes, valve VTA conducts and TA operates. Capacitor C1 is now charged in the grid circuit of VTA by the peaks of the rectified supply until after a few half-cycles the grid potential becomes sufficiently negative to cut off VTA, whereupon TA falls back and switch SA steps to position 2. Capacitor C1 discharges through the resistance cross-connected at RAO according to the plan in operation to determine the redamber offset period. Relay TA then reoperates and steps SA to position 3 in which ASA energizes to give amber to phase A in addition to the red given to both phases when the power was switched on. Timing takes place over RA and SA then advances to position 4 in which ASB energizes to give green to phase A and red to phase B, and timing takes place over IG according to the plan in operation. SA now goes to position 5 in which no change occurs but the green limit period is timed over GL. At the end of this period, or sooner if the master controller is operating, SA advances to position 6 and connects up TB to prepare for the stepping of SB to control phase B. The use of independent switches allows the ready insertion of additional phases, e.g. for pedestrians crossing or for turning traffic. Relays AH, BH prevent the firing of false signals should either switch be moved manually.  Control from master controller.-In accordance with the plan in operation a number of pulses are received by relay A at the beginning of each cycle, and a reversed pulse at the middle of the cycle operates relay B. The A pulses step switch SC and at the end of the train one of relays PA ... PD energizes. If no A pulses are received PA is operative. The operation of AX at the first, pulse starts the offset A timer, and capacitor C5, which is already charged, discharges until valve VOA becomes conductive and OA energizes provided switch SA is in position 5. This results in SA stepping to position 6, ending the green limit period for phase A and starting the amber. The B pulse operates relay BX to start the offset B timer which ends the green limit period for phase B. Switch SC homes in readiness for the next train of A pulses. If switch SC is set to position 7, relays FA, FB energize and connect up both ASA, ASB to light the amber lamps of both phases. Also, relay F operates intermittently under the control of capacitors C3, C9 in association with a double triode VF to flash the lamps by means of relay FL, the flashing rate being adjustable. Switch SC is set to position 8 to release FA, FB. Manual control switch FS.-This may be set to four positions: (1) off (no signals), (2) normal automatic operation, (3) control by push buttons such as PBA, PBB, (4) flashing amber signals only. Main controller, Figs. 6-8.-Relay IT controlled by a pair of capacitors 1C1, 1C2 and a double triode V1T energizes twice per cycle at intervals which are adjustable manually by the switches shown and connects up 1A, 1B alternately. The phase split for the main phases is adjustably determined by switch PSS. Relay 1T connects up start relay 1ST and switch M steps with the assistance of relays 1CD, 1P sending pulses over the line L1, L2 until it reaches a position marked by one of the plan keys. Relay 1CD is now held and switch M homes. When IT energizes next 1B is up, rendering the other wiper of PSS effective, and 1P operates to send a reversed pulse since 1ST is back. It is assumed that four plans are provided to cater for light, medium and heavy traffic and for emergency operation, these corresponding to keys KLP, KMP, KHP, KEP and plan relays 1PA ... 1PD which control indicating lamps. During emergency operation,. relay PD, Fig. 4, is effective to give right of way permanently to phase A. Key KAM permits change over to automatic operation under the control of equipment ATE which may connect up different plans according to a time schedule or according to the density of traffic at certain points. Keys KFA-ON, KFA-OFF control the starting and ending of flashing amber working.